A problem:
Aside from placing an ad on this site your best option is a local sale. I've sold two boats posting notices in supermarkets, local marinas, chandleries (I know, Arizonia. But sources say there are more boats in Arizona per capita than any other state).
Speaking of local... Is there a trailer? That would change your strategy. Local becomes much larger.
You could find facebook groups for O'day owners, sailors or whatever to post on.
Sailboatsforsale.com is another option. For the commission on an older sailboat, brokers will list it but not spend much money on marketing it.
You really need to become your own boat seller. When I lived on the North Fork of LI people would haul a boat to some place on the Main road, put a sign on it and hope for the best. It kinda worked.
In my opinion, with any marketing you do don't bother with listing all the features you think are important to a buyer. Try to sell the potential of what the boat could do for a potential buyer. "Family fun" "Adventure on the cheap" "See the Powell treasures on a budget" "Tour without high fuel costs" or something like that. No one you are trying to entice cares about the details of the scuppers. As is said about steak .. sell the sizzle.